Refrigeration cycle device

ABSTRACT

A mixed refrigerant including a plurality of component refrigerants circulates in a refrigeration cycle device. An expansion valve includes a power element. A filled fluid filled in the power element is one component refrigerant in the plurality of component refrigerants. A slope of a saturated vapor pressure curve of the filled fluid is larger than the slope of the saturated vapor pressure curve SV 0  of the mixed refrigerant. Thereby, an opening degree of the expansion valve can be prevented from exceeding in a low-temperature region, and the opening degree corresponding to a load can be obtained in a high-temperature region.

CROSS REFERENCE TO RELATED APPLICATION

The present application is based on Japanese Patent Application No.2008-196320 filed on Jul. 30, 2008, the disclosure of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a refrigeration cycle device with amixed refrigerant.

BACKGROUND OF THE INVENTION

A refrigeration cycle device is disclosed in JP-A-2007-071461,corresponding to US 2007/074538, for example. In the refrigeration-cycledevice, a compressor, a condenser, an expansion valve and an evaporatorare circularly-connected. The refrigeration cycle device furtherincludes an internal heat exchanger for exchanging heat between ahigh-pressure refrigerant, which flows between the condenser and theexpansion valve, and a low-pressure refrigerant, which flows between theevaporator and the compressor. A refrigerant circulating in therefrigeration cycle device is a single refrigerant or a mixedrefrigerant. A temperature-sensitive expansion valve is widely used asthe expansion valve.

JP-A-2-203175 discloses a refrigeration cycle device using a mixedrefrigerant, and a temperature-sensitive expansion valve. Furthermore,JP-A-2-203175 discloses that a refrigerant that is the same with acirculating refrigerant in the refrigeration cycle device or arefrigerant having a pressure-temperature property similar to that ofthe circulating refrigerant is filled in a temperature-sensitive portionof the expansion valve. The refrigerant filled in thetemperature-sensitive portion is referred to as a filled fluid.

Temperature-sensitive expansion valves having various configurations aregenerally known. For example, JP-A-2-203175 discloses a joint-typeexpansion valve including a joint portion for connecting to a pipeconfiguring the refrigeration cycle device. JP Patent No. 4039069discloses a box-type expansion valve including a housing, in which ahigh-pressure passage and a low-pressure passage are formed.JP-U-7-40139 discloses a cassette-type structure, in which atemperature-sensitive portion and a valve portion are unitized.JP-A-2-203175 further discloses an internal-equalizing expansion valvethat draws a pressure between the expansion valve and an evaporator.JP-U-7-40139 discloses an external-equalizing expansion valve that drawsa pressure between an evaporator and a compressor.

The conventional temperature-sensitive expansion valve controls a stateof the refrigerant at an outlet portion of the evaporator. For example,the temperature-sensitive expansion valve controls such that the degreeof superheat of the refrigerant circulating in the refrigeration cycledevice at the outlet portion of the evaporator becomes a predeterminedvalue.

However, in the case where the mixed refrigerant is used as therefrigerant circulating in the refrigeration cycle device, a pressuredifference between a saturated vapor pressure curve of the circulatingrefrigerant and a valve-opening property depending on a saturated vaporpressure curve of the filled fluid may show an undesirable increase ordecrease in a low-temperature region or a high-temperature region. Thebehavior appears prominently when the filled fluid and the; circulatingrefrigerant are different. Thereby, a desired control property may notbe obtained in the low-temperature region or the high-temperatureregion.

For example, in the case where the pressure difference between thesaturated vapor pressure curve of the circulating refrigerant and thevalve-opening property increases as the temperature decreases, theexcess pressure difference is obtained, and thereby, the expansion valveopens beyond necessity. When the opening degree of the expansion valvebecomes excessively large, the liquid back occurs. Thereby, the controlof the degree of superheat is broken, and the refrigeration capacity maybe decreased.

Because thermally load is large in the high-temperature region, it ispreferable that the flow amount of the circulating refrigerant isincreased. However, in the case where the pressure difference betweenthe saturated vapor pressure curve of the circulating refrigerant andthe valve-opening property decreases as the temperature increases, thepressure difference becomes too little. Thereby, the expansion valve maynot obtain the necessary opening degree.

SUMMARY OF THE INVENTION

In view of the above points, it is an object of the present invention toprovide an improved refrigeration cycle device with a mixed refrigerant.

It is another object of the present invention to provide a refrigerationcycle device, in which a mixed refrigerant circulates, that can stablyoperate in a low-temperature region or a high-temperature region.

Furthermore, it is another object of the present invention to provide arefrigeration cycle device, in which a mixed refrigerant circulates,that can stably operate in a range from a low-temperature region to ahigh-temperature region.

According to one aspect of the present invention, a refrigeration cycledevice includes a refrigerant cycle including a compressor, a condenser,an expansion valve and an evaporator, which are coupled in this order;and a mixed refrigerant made of a plurality of component refrigerants,which is circulated in the refrigerant cycle. The expansion valveincludes a valve portion configured to adjust an amount of the mixedrefrigerant supplied into the evaporator based on an opening degree ofthe valve portion, and a power element configured to adjust the openingdegree of the valve portion based on a pressure of a filled fluid thatis filled inside the power element. A slope of a saturated vaporpressure curve of the filled fluid is larger than a slope of a saturatedvapor pressure curve of the mixed refrigerant.

In the above configuration, the opening degree, which corresponds to aload, of the expansion valve can be obtained. When the slope of thesaturated vapor pressure curve of the filled fluid is larger than theslope of the saturated vapor pressure curve (SV0) of the mixedrefrigerant, the opening degree of the expansion valve can be preventedfrom exceeding in a low-temperature region. When the slope of thesaturated vapor pressure curve of the filled fluid is larger than theslope of the saturated vapor pressure curve (SV0) of the mixedrefrigerant, the opening degree of the expansion valve can be preventedfrom becoming too little in a high-temperature region.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

FIG. 1 is a schematic diagram showing a refrigeration cycle deviceaccording to an embodiment of the present invention;

FIG. 2 is a temperature-pressure graph showing a saturated vaporpressure curve of a refrigerant according to the embodiment of thepresent invention;

FIG. 3 is a temperature-pressure graph showing a vapor pressure of afilled fluid in a power element of an expansion valve; and

FIG. 4 is a temperature-pressure graph showing a characteristic of avalve-open pressure in the expansion valve.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment

Hereinafter, an embodiment that is applied to a refrigeration cycledevice 10 of a refrigerator will be described. As shown in FIG. 1, therefrigeration cycle device 10 includes a compressor 20, a condenser 30,an expansion valve 40 and an evaporator 50. These components areconnected by plural pipes in this order to form a closed circuit. In therefrigeration cycle device 10, an internal heat exchanger 60 forexchanging heat between a high-pressure refrigerant, which flows betweenthe condenser 30 and the expansion valve 40, and a low-pressurerefrigerant, which flows between the evaporator 50 and the compressor20.

The refrigeration cycle device 10 is used for the refrigerator. Arefrigerant is compressed by the compressor 20 to become the hightemperature and high pressure refrigerant. The compressor 20 is drivenby an internal combustion engine or an electric motor. A fixed-capacitytype compressor or a variable-capacity type compressor may be used asthe compressor 20. The condenser 30 is a high-pressure side heatexchanger. The condenser 30 is coupled to a discharge portion of thecompressor 20. The refrigerant is condensed by exchanging heat withambient air to become liquid. The expansion valve 40 is a decompressor.The expansion valve 40 decompresses the liquid refrigerant flowing outof the condenser 30 in iso-enthalpy and expands the refrigerant. Theexpansion valve 40 controls the throttle opening degree such that astate of the refrigerant at an outlet portion of the evaporator 50becomes a predetermined state. The expansion valve 40 is atemperature-sensitive expansion valve that detects the state of therefrigerant based on a temperature. The evaporator 50 is a low-pressureside heat exchanger, and is referred to as a cooler or a heat absorber.The evaporator 50 cools air in a freezer as an object to be cooled byevaporating the refrigerant in the evaporator 50.

The expansion valve 40 will be described with reference to FIG. 1. Anexternal-equalizing expansion valve is used as the expansion valve 40.The expansion valve 40 includes a valve portion 41 that adjusts theamount of the refrigerant supplied into the evaporator 50, and a powerelement 42 that adjusts the opening degree of the valve portion 41. Thevalve portion 41 is configured by a valve seat, a valve disc and avalve-closing spring. The power element 42 as a temperature-sensitiveportion is a fluid pressure type device that can function as a detectionportion for detecting the state of the refrigerant at the outlet portionof the evaporator 50, a control portion for controlling an operationdegree of the valve portion 41 such that the state of the refrigerantcorresponds to a target state, and a drive portion for adjusting theopening degree of the valve portion 41 depending on the operationdegree.

The power element 42 includes a diaphragm 43 as a pressure-sensitivemember. The diaphragm 43 is divided into a first chamber 44 and a secondchamber 45. A valve shaft 46 for driving the valve disc is connected tothe diaphragm 43. The diaphragm 43 is displaced by a differentialpressure between the first chamber 44 and the second chamber 45, andadjusts the opening degree of the valve portion 41. The first chamber 44is communicated with a temperature-sensitive tube 48 through a pipe 47,and forms an enclosed space. A fluid is filled in the first chamber 44.The filled fluid in the first chamber 44 is a two-phase refrigerant andauxiliary gas for adjusting condition of the refrigerant. Thetemperature-sensitive tube 48 is provided in contact with a pipe in thevicinity of the outlet portion of the evaporator 50. Thereby, thetemperature of the refrigerant at the outlet portion of the evaporator50 is conducted to the filled fluid in the first chamber 44. The filledfluid detects the temperature of the refrigerant at the outlet portionof the evaporator 50. The filled fluid changes a pressure of the firstchamber 44 depending on the temperature of the refrigerant at the outletportion of the evaporator 50. The second chamber 45 is communicated witha passage in the vicinity of the outlet portion of the evaporator 50through a pipe 49. Thereby, an evaporating pressure of the refrigerantin the evaporator 50 is introduced into the second chamber 45. In theexpansion valve 40, the diaphragm 43 is displaced by a differentialpressure between the evaporating pressure in the evaporator 50 and thepressure depending on the temperature of the refrigerant at the outletportion of the evaporator 50.

A circulating refrigerant is a mixed refrigerant that is made by mixingplural component refrigerants. Saturated vapor pressure curves of therespective plural component refrigerants are different each other. Thecirculating refrigerant may include three or more componentrefrigerants. The mixed refrigerant includes a first componentrefrigerant, a second component refrigerant and a third componentrefrigerant. The boiling points of the component refrigerants decreasein the following order; the first component refrigerant, the secondcomponent refrigerant, and the third component refrigerant. The filledfluid in the power element 42 is only one component refrigerant.Thereby, the refrigerant can be easily filled in the power element 42.

FIG. 2 to FIG. 4 are temperature-pressure graphs, in which thehorizontal axis indicates a temperature T (° C.) and the vertical axisindicates a pressure P (MPa). FIG. 2 shows a saturated vapor pressurecurve SV0 of the mixed refrigerant, and saturated vapor pressure curvesSV1, SV2, SV3 of the respective component refrigerants. As shown in FIG.2, a saturated vapor pressure of the first component refrigerant is thehighest, and a saturated vapor pressure of the third componentrefrigerant is the lowest. The saturated vapor pressure curve SV0 of themixed refrigerant is located between the saturated vapor pressure curvesof the two component refrigerants, which have the relatively lowsaturated vapor pressures. Specifically, the saturated vapor pressurecurve SV0 of the mixed refrigerant is located between the saturatedvapor pressure curve SV2 of the second component refrigerant and thesaturated vapor pressure curve SV3 of the third component refrigerant.

A slope of the saturated vapor pressure curve SV1 of the first componentrefrigerant is the largest, and a slope of the saturated vapor pressurecurve SV3 of the third component refrigerant is the smallest. The slopeof the saturated vapor pressure curve SV1 of the first componentrefrigerant, which corresponds to the filled fluid, is larger than aslope of the saturated vapor pressure curve SV0 of the mixed refrigerantin a range from a low-temperature region to a high-temperature region. Aslope of the saturated vapor pressure curve SV2 of the second componentrefrigerant is larger than the slope of the saturated vapor pressurecurve SV0 of the mixed refrigerant in the range from the low-temperatureregion to the high-temperature region. The slope of the saturated vaporpressure curve SV3 of the third component refrigerant is smaller thanthe slope of the saturated vapor pressure curve SV0 of the mixedrefrigerant in the range from the low-temperature region to thehigh-temperature region.

A saturated vapor pressure difference SD between the saturated vaporpressure curve SV1 of the first component refrigerant and the saturatedvapor pressure curve SV0 of the mixed refrigerant gradually increases asan evaporation temperature increases. Thereby, a saturated vaporpressure difference SD2 in a high-load temperature is larger than asaturated vapor pressure difference SD1 in a low-load temperature. Inthe present embodiment, the high-load temperature is −10° C. and thelow-load temperature is −40° C.

As a comparative example, a saturated vapor pressure curve SVC of acomparative refrigerant is shown in FIG. 2. The comparative refrigerantdiffers from the component refrigerants of the mixed refrigerant. Whenthe comparative refrigerant is used for the filled fluid, the slope ofthe saturated vapor pressure curve SVC is smaller than the slope of thesaturated vapor pressure curve SV0 of the mixed refrigerant.

FIG. 3 illustrates a characteristic curve showing a vapor pressure ofthe fluid after auxiliary gas such as helium is added to the respectivecomponent refrigerants. The characteristic curve in FIG. 3 is adjustedby the auxiliary gas such that the circulating refrigerant is controlledto be a predetermined state at a temperature of −30° C., which is astandard temperature for the refrigerator. A characteristic curve SV1+shows the characteristic after the first component refrigerant isadjusted. A characteristic curve SV2+ shows the characteristic after thesecond component refrigerant is adjusted. A characteristic curve SV3+shows the characteristic after the third component refrigerant isadjusted. A characteristic curve SVC+ shows the characteristic after thecomparative refrigerant is adjusted. The slope of the saturated vaporpressure curve of the respective component refrigerants can be kept evenwhen the adjustment by the auxiliary gas is performed.

FIG. 4 illustrates a characteristic curve showing a valve-open pressurebased on bias force such as the valve-closing spring of the expansionvalve 40. A characteristic curve SV1D shows the valve-opencharacteristic of the filled fluid including the first componentrefrigerant. A characteristic curve SVCD shows the valve-opencharacteristic of the filled fluid including the comparativerefrigerant.

A slope of the characteristic curve SVCD is smaller than a slope of thecharacteristic curve SV1D. Thus, the characteristic curve SVCD islocated at a higher pressure side than the characteristic curve SV1D inthe low-temperature region that is lower than the standard temperature.In the low-temperature region, the characteristic curve SVCD is awayfrom the saturated vapor pressure curve SV0 of the mixed refrigerant inthe pressure axis direction. That is, a pressure difference between thecharacteristic curve SVCD and the saturated vapor pressure curve SV0increases as a temperature increases in the low-temperature region. Thecharacteristic curve SVCD has a pressure difference PD1, which is largerthan a pressure difference PD0 at the standard temperature, in thelow-temperature region. Thereby, the excessive pressure difference isgenerated in the low-temperature region, and the opening degree becomesexcessively large. The characteristic curve SVCD is located at a lowerpressure side than the characteristic curve SV1D in the high-temperatureregion that is higher than the standard temperature. The characteristiccurve SVCD has a pressure difference PD2, which is smaller than thepressure difference PD0 at the standard temperature, in thehigh-temperature region. Thereby, when the characteristic curve SVCD isused, the opening degree becomes insufficient in the high-temperatureregion.

In contrast, in the characteristic curve SV1D, the pressure differencegradually increases from the low-temperature region to thehigh-temperature region. The characteristic curve SV1D has a pressuredifference PD3, which is smaller than the pressure difference PD0 at thestandard temperature, in the low-temperature region. The characteristiccurve SV1D has a pressure difference PD4, which is larger than thepressure difference PD0 at the standard temperature, in thehigh-temperature region. Thereby, the opening degree of the expansionvalve 40 gradually increases from the low-temperature region to thehigh-temperature region.

In the present embodiment, R404A is used as the mixed refrigerant. Themixed refrigerant R404A includes R125 as the first componentrefrigerant, R143a as the second component refrigerant and R134a as thethird component refrigerant. The filled fluid is R125 that is the firstcomponent refrigerant. As the comparative refrigerant, R22 is used.

When the refrigeration cycle device 10 is driven, the expansion valve 40adjusts the opening degree of the valve portion 41 such that the stateof the refrigerant at the outlet portion of the evaporator 50corresponds to the target state. The refrigeration cycle device 10 asthe refrigerator can drive in the range from the low-temperature regionto the high-temperature region of the evaporation temperature. In thevicinity of −40° C. of the low-load temperature corresponding to alow-load state as the refrigerator is regarded as a very low-temperaturein the evaporation temperature of the refrigerator. In the vicinity ofthe low-load temperature, a flow amount of the refrigerant decreases andthe opening degree of the expansion valve 40 also decreases. Incontrast, in the vicinity of −10° C. of the high-load temperaturecorresponding to a high-load state as the refrigerator, a large quantityof the refrigerant corresponding to the high-load is allowed to flow.

The slope of the saturated vapor pressure curve of the componentrefrigerant selected as the filled fluid is larger than the slope of thesaturated vapor pressure curve of the mixed refrigerant as thecirculating refrigerant when the evaporation temperature is in thelow-temperature region, particularly, in the very low-temperatureregion. Thereby, the opening degree of the expansion valve 40 can beprevented from exceeding the opening degree based on the load in thelow-temperature region, particularly, in the very low-temperatureregion. The large slope in the low-temperature region affects thepressure change and the opening degree change sufficiently with respectto the temperature change. Therefore, the stable control can be kept inthe range of the small opening degree in the vicinity of the low-loadtemperature, and the control of the degree of superheat can be stablycontrolled even in the low-temperature region, specifically, in the verylow-temperature region.

It is preferable that the saturated vapor pressure curve of thecomponent refrigerant selected as the filled fluid is similar to thesaturated vapor pressure curve SV0 of the mixed refrigerant when theevaporation temperature is in the high-temperature region. Thereby, therelatively-large opening degree corresponding to the high-load can beobtained and the opening degree of the expansion valve can be preventedfrom exceeding the opening degree based on the load in thehigh-temperature region including the high-load temperature. Therefore,the liquid back can be avoided and the stable driving can be operated inthe high-temperature region.

Other Embodiments

The present invention is not limited to the above embodiment, and can bemodified variously as follows. In the above embodiment, therefrigeration cycle device using R404A as the circulating refrigerant isdescribed. However, a refrigeration cycle device using various mixedrefrigerants as the circulating refrigerant may be used. Moreover, arefrigeration cycle device using plural refrigerants as the filled fluidmay be used. One component refrigerant or plural component refrigerantsother than the component refrigerant having the smallest slope of thesaturated vapor pressure curve may be used as the filled fluid. Forexample, the second component refrigerant R143a may be used as thefilled fluid. The present invention can be applied to a joint-typeexpansion valve or a box-type expansion valve. The present invention canbe applied to an internal-equalizing expansion valve or anexternal-equalizing expansion valve. The present invention can beapplied to an expansion valve having a cassette-type structure.Furthermore, the present invention can be applied to a refrigerationcycle device having an ejector.

While the invention has been described with reference to preferredembodiments thereof, it is to be understood that the invention is notlimited to the preferred embodiments and constructions. The invention isintended to cover various modification and equivalent arrangements. Inaddition, while the various combinations and configurations, which arepreferred, other combinations and configurations, including more, lessor only a single element, are also within the spirit and scope of theinvention.

1. A refrigeration cycle device comprising: a refrigerant cycleincluding a compressor, a condenser, an expansion valve and anevaporator, which are coupled in this order; and a mixed refrigerantmade of a plurality of component refrigerants, which is circulated inthe refrigerant cycle, wherein the expansion valve includes: a valveportion configured to adjust an amount of the mixed refrigerant suppliedinto the evaporator based on an opening degree of the valve portion; anda power element configured to adjust the opening degree of the valveportion based on a pressure of a filled fluid that is filled inside thepower element, and a slope of a saturated vapor pressure curve of thefilled fluid is larger than a slope of a saturated vapor pressure curveof the mixed refrigerant.
 2. The refrigeration cycle device according toclaim 1, wherein the filled fluid is one component refrigerant of theplurality of component refrigerants, and a slope of a saturated vaporpressure curve of the one component refrigerant is larger than the slopeof the saturated vapor pressure curve of the mixed refrigerant.
 3. Therefrigeration cycle device according to claim 2, wherein the slope ofthe saturated vapor pressure curve of the one component refrigerant isthe largest in the plurality of component refrigerants.
 4. Therefrigeration cycle device according to claim 1, wherein a slope of asaturated vapor pressure curve of one component refrigerant is thesmallest in the plurality of component refrigerants, and the filledfluid is made of at least one of the plurality of component refrigerantsother than the one component refrigerant.
 5. The refrigeration cycledevice according to claim 1, wherein the filled fluid is one componentrefrigerant in the plurality of component refrigerants.
 6. Therefrigeration cycle device according to claim 1, wherein the slope ofthe saturated vapor pressure curve of the filled fluid is larger thanthe slope of the saturated vapor pressure curve of the mixed refrigerantin a general range from a low-temperature region to a high-temperatureregion.
 7. The refrigeration cycle device according to claim 1, whereina saturated vapor pressure difference between the saturated vaporpressure curve of the filled fluid and the saturated vapor pressurecurve of the mixed refrigerant gradually increases as an evaporationtemperature increases.